1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to a front light emitting type organic electroluminescent display device with a first electrode having a concentration gradient which functions as a pixel electrode and a black matrix at the same time, and a method of fabricating the front light emitting type organic electroluminescent display device.
2. Description of the Related Art
FIG. 1A illustrates the cross-sectional structure of a conventional front light emitting type organic electroluminescent (EL) display device. FIG. 1B illustrates the plan structure of a conventional organic electroluminescent display device. FIG. 1A illustrates the cross-sectional structure taken along the line I—I of FIG. 1B.
Referring to FIG. 1A and FIG. 1B, a transparent insulation substrate 10 is divided into a first region 11 in which a pixel electrode is formed, and a second region 12 in which a thin film transistor (TFT) and a capacitor are formed. The second region 12 includes a semiconductor layer 20 in which source/drain regions 21 and 22 are formed, a thin film transistor equipped with a gate electrode 31 and source/drain electrodes 51 and 52, and a capacitor equipped with a first electrode 32, and a second electrode 53 connected to the source electrode 51 of the thin film transistor.
A gate insulating layer 30 is formed in a space between the semiconductor layer 20 and the gate electrode 31.
An interlayer insulating layer 40 is formed in a space between the gate electrode 31 and the source/drain electrodes 51 and 52.
A pixel electrode 70 connected to one of the source/drain electrodes 51 and 52, e.g., the drain electrode 52 through a via hole 61, is formed on a passivation layer 60 of the first region 11 as an anode electrode. A planarization layer 80 equipped with an opening part 81 which exposes a portion of the pixel electrode 70 is formed on the pixel electrode 70. An organic EL layer 90 is formed in the opening part 81, and a transparent electrode 95 is formed on the organic EL layer 90 as a cathode electrode.
References 35, 55 and 56 of FIG. 1B represent gate lines, data lines and power supply lines, respectively.
In the above described conventional front light emitting type organic electroluminescent display device, contrast deteriorates because a material having a high reflection ratio is used, thereby reflecting an external light through a metal wiring material, particularly a metallic material for source/drain electrodes.
Although the external light can be prevented from being reflected by adhering a polarizer onto a front of the conventional organic electroluminescent display device, using the polarizer is expensive, and a luminance of the organic electroluminescent display device is lowered because a transmittancy of light emitted from an organic electroluminescent (EL) layer of the organic electroluminescent display device is lowered by the polarizer. Furthermore, a life cycle of the organic EL layer is shortened where a current flowing through the conventional organic electroluminescent display device is increased to improve the luminance of the organic electroluminescent display device.